Skis, including snowboards, are by commercial necessity designed to accommodate a range of rider sizes, weights, riding styles, and skiing conditions. A particular model of ski therefore must meet numerous, and sometimes conflicting, design criteria.
For example, it is desirable for a ski to be stable and perform well in snow conditions ranging from powder to ice. An ideal powder ski is one with a relatively soft flex. On the other hand, a ski must be considerably stiffer, both longitudinally and torsionally, for satisfactory performance in icy conditions. At the same time, a particular ski must accommodate riders within a range of weights, while maintaining satisfactory camber characteristics. The camber of a ski determines what portion of the base is normally in contact with the snow, and further determines the turning characteristics of the ski. A ski is shaped to induce a turn when an edge is pressed into contact with the snow. To achieve this characteristic, the lateral edges are designed with sidecut in the center portion of the ski; that is, the lateral width of the ski is greater on the ends than in the center. The greater the amount of sidecut, the more readily the ski will turn when the edge of the center portion of the ski is pressed into contact with the snow. In this way, the camber and the flexing characteristics of the ski interact to determine the turning characteristics of the ski.
In addition, a ski is ideally designed to be responsive to changes in the snow surface, to skier inputs, and to isolate the skier from shock and vibration to the greatest degree possible. A responsive ski is one which is relatively stiff, and has a relatively low inertial moment. Unfortunately, stiffness and a low inertial moment detract from skier comfort by causing a ski to "chatter", that is for the tip and tail of the ski to rebound away from the snow, causing a momentary loss of control. A chattering ski also will transmit uncomfortable levels of vibration to the skier, predominantly through the binding into the skier's feet. These continual vibrations lead to fatigue, and possibly contribute to injuries.
Ski designers therefore attempt to design damping into a ski provide a degree of comfort and control for the skier. The damping usually is achieved by incorporating rubber, lead, or other deadening materials into the body of the ski. This solution adds to the weight and inertial moment of the ski, reducing its responsiveness. Additionally, a ski is typically designed with a less than ideal amount of stiffness as a further concession to skier comfort.
A satisfactory resolution of these problems is even more complicated in a type of ski known as a snowboard. A snowboard incorporates certain characteristics of a surfboard into a ski for use on snow. A rider stands on a snowboard facing generally to one side. The rider's feet are secured to the snowboard, one in front of the other, by two bindings in the center portion of the board. As a result of this riding position, the rider is unable to exert equal turning forces on both edges of the ski. When turning in one direction, the rider bears on one edge of the board with the toes and balls of his feet, while bearing with his heels when turning in the opposite direction. A rider is usually able to exert less turning force through the heels, leading to a reduced turning ability in one direction. Snowboard manufacturers have responded to this problem by designing "asymmetric" boards, i.e. having different amounts of sidecut in opposite edges of the snowboard. A greater sidecut in the "heel turning" edge of the board requires the rider to exert less force on the edge for a turning ability equal to the "toe turning" side of the board. The asymmetry of such boards detracts, however, from the straight line stability and speed of the board.
Design problems and resulting performance compromises such as these have lead to a efforts to design a ski damping system which allows a ski to reach a maximum level of performance under a range of snow and riding conditions, while providing maximum rider comfort, control, and turning ability.
An adjustable flex ski is disclosed in U.S. Pat. No. 4,577,886 to Powers in which three adjustable tensile members are embedded in the below the neutral plane in the body of the ski. The tensile members can be independently adjusted to change the flex characteristics of portions of the ski to adjust the stiffness of the ski. U.S. Pat. No. 4,221,400 discloses a ski having pre-stressed, curved tensile members embedded in the ski body. The flex of the ski is adjusted by rotating the tensile members, thereby changing the orientation of the curvature of the tensile members, and their resistance to flexing vertically in relation to the ski.
A ski having adjustable camber-flattening resistance is disclosed in U.S. Pat. No. 4,300,786 to Alley. The '786 ski utilizes inserts disposed in internal voids in the central portion of the ski to adjust the camber-flattening resistance of the ski. U.S. Pat. No. 4,740,009 discloses a ski having an internal apparatus for adjusting the camber of the ski. The apparatus includes a sensor for sensing the degree of flex, and for controlling a motorized flex adjustment mechanism.
U.S. Pat. No. 3,260,531 to Heuvel discloses a terrain conforming ski in which the mechanism for mounting the binding to the ski permits fore and aft adjustment for redistributing the body weight of the skier to adapt the ski to different snow conditions.
U.S. Pat. No. 4,951,960 to Sadler and U.S. Pat. No. 4,565,386 to Crainich disclose skis having longitudinal slits extending partially along the length of the ski. In each case, the slit allows an additional edge to be brought to bear against the snow surface to enhance the turning characteristics of the ski.
A need remains, therefore, for an improved damping apparatus for a ski which provides for the ready adjustment of the longitudinal and torsional flex characteristics of a ski; which further provides for ready adjustment of the camber of a ski; and which further provides for effective damping of deflections and associated vibrations of the ski which contribute to a loss of control and skier discomfort, fatigue, and injury.